This invention relates to a method and apparatus for moving heat-treated parts into, through, and out of a fluid-containing tank while avoiding nicking of parts. In particular, the invention relates to the movement of parts into, through, and out of a quench or cooling tank of a continuous furnace hardening or carburizing system while preventing any part-to- part contact.
Existing continuous hardening furnace systems typically include a hardening furnace, a quench press whose operation includes initial quenching, a secondary quenching or cooling tank for core cooling, a washer (if required), and a tempering furnace. Parts which are processed through these systems are usually charged into, and transported through, the hardening furnace on trays, then are unloaded from the trays and moved through the remaining furnace system stages. The parts are moved from stage to stage automatically by a variety of mechanisms.
With many of the parts that are processed in hardening furnace systems, such as bearing races, it is very important that all part-wearing surfaces remain smooth. If during processing physical damage (nicking) occurs on a wearing surface to a depth greater than the amount of material to be removed from the wearing surface by subsequent finish grinding operations, the part has to be rejected. A problem with known hardening furnace systems is that at various stages parts can come into contact with one another, resulting in part nicking. Due to the need to reject many of such nicked parts, part nicking can dramatically impair the productivity of the furnace system.
In general, since parts are contained on trays until being discharged from the hardening furnace they remain separated and hence are not prone to nicking due to part-to-part contact. From the point of unloading and onward, however, part-to-part contact and the accompanying nicking became a concern.
In typical hardening furnace systems the transfer of parts from the quench press to the secondary quench tank or cooling tank requires a drop in elevation of the parts. Known hardening furnace systems simply allow the heat-treated parts to fall freely the necessary distance to transfer the parts from the quench press to a conveyor at the bottom of the secondary quench tank. Clearly, with such a practice, there is a high probability of falling parts coming into contact with one another and with the downstream parts below.
Once parts reach the bottom of the quench tank of prior art hardening furnace systems, the parts are directed through the quenching liquid (e.g., oil or water) by means of an upwardly-sloped conveyor which moves the parts to the top of the tank in preparation for transfer of the parts to a washer or a temper furnace. There is then another free fall and further risk of nicking when the parts are delivered from the secondary quench tank to a conveyor leading to the washer or temper furnace.
It is therefore an object of the present invention to provide apparatus for avoiding part-to-part contact, and hence part nicking, in a portion of a furnace system.
It is also an object of the present invention to decrease the part reject rate of hardening furnace systems by reducing part nicking.
It is yet another object of the invention to provide a method and apparatus by which heat-treated metal parts are moved into, through, and out of a secondary quench tank of a hardening furnace system while avoiding part-to-part contact.